1. Field of the Invention
The present invention relates to an optical memory device for recording, erasing, and reproducing information by the light, and more particularly to an optical memory device which is made of a photochromic material as a recording film.
2. Description of the Related Art
In a conventional optical memory device made of a photochromic material, the photochromic material is dispersed in a polymeric binder for use. For example, Japanese Unexamined Patent Publication No. SHO 64-87684 discloses an optical memory device in which a recording film consisting of a polymeric binder with a photochromic material is formed on the substrate. The formation of the recording film is carried out in accordance with the following procedures: First, photochromic materials, such as derivatives of diarylethene, and polymeric binder, such as PMMA (polymethylmethacrylate) or polystyrene, are dissolved or dispersed in an appropriate solvent; the resultant solution is spread on the surface of the glass substrate or the like by spin coating; and then the solvent is evaporated.
However, in the conventional constitution and the formation process of the recording film mentioned above, it needs the solvents in which the photochromic material and the polymeric binder are dissolved. Moreover, it also needs annealing process or like procedure to evaporate the solvent after the solution is spread on the substrate, which makes the film-forming process more complicated.
For the polymeric binder, it is desirable to adopt a material which exhibits excellent weather proof such as a three dimensionally cross-linked polymer. However, the cross-linked polymers cannot be adopted in the conventional constitution because of its insolubility. Consequently, in conventional formation, a photochromic material in the recording film easily deteriorates and shows unsatisfactory photochromic durability.
In order to overcome such the problem, several methods have been proposed, in which an ultraviolet-curing resin is adopted as the polymeric binder. In case that a typical ultraviolet-curing epoxy resin is adopted as the polymeric binder, however, the durability of the photochromic material also deteriorated in short time. For this reason, this method was not available for practical use.